Final answer:
An improvement crossing over into adjacent property without permission is called an encroachment. It often leads to disputes and may necessitate legal action. Encroachments include things like fences or driveways extending onto another's property.
Step-by-step explanation:
An improvement which crosses over the adjacent property without the permission of the owner is known as an encroachment. Encroachments can lead to disputes between property owners and may require legal resolution. Common examples include a neighbor's fence, shed, or driveway extending beyond their property line and into someone else's property. To address the issue of an encroachment, property owners may need to engage in negotiations, seek mediation, or ultimately resolve the dispute through legal action.